Recently, a capacitive type and an optical type are widely used in a fingerprint sensor.
In general, a capacitive type fingerprint sensor recognizes a fingerprint by sensing capacitance formed by a fingerprint of the human body using a semiconductor device sensitive to a voltage and current. An optical type fingerprint sensor has an advantage of good durability and is configured to include an optical source and an optical sensor. The optical sensor is configured to sense a fingerprint of a user by sensing light emitted from the optical source.
FIG. 1 is a cross-sectional view of a conventional optical fingerprint sensor.
As shown in FIG. 1, in the conventional optical fingerprint sensor, an optical source 110 and an optical sensor 120 are disposed at a specific distance and angle. When light 111 from the optical source 110 is reflected by a fingerprint 130 of a user, the optical sensor 120 can obtain the form of the fingerprint 130 by sensing the light 111 reflected by the fingerprint 130.
If the distance between a fingerprint and a surface of the sensor is distant, however, the conventional optical fingerprint sensor is configured so that pieces of light reflected by adjacent fingerprints are easy to be introduced.
Accordingly, the conventional optical fingerprint sensor had a problem in that it did not obtain a clear fingerprint image because pieces of light reflected from fingerprints are mixed if the distance between a fingerprint and a surface of a sensor is 10 um or more.